When a passenger puts their bags through an X-ray machine, they go through a type of electromagnetic energy. Unlike visible light, humans cannot see X-rays. In hospitals, these X-ray energy beams can see through skin tissue to detect broken bones, tumors or other injuries. In an airport, X-ray technology is used in CT (computer tomography) scanners. Suitcases from passengers ride along a conveyor belt and pass through the hollow CT scanning machines. The X-rays bounce off the objects inside the suitcases, measuring the density and mass of each object. All that data is immediately entered into a computer. CT scanners are more complex than metal detectors and can analyze chemical components in addition to metallic objects. If the density and mass of items in the suitcase matches items that are known to be dangerous, the objects are removed from the suitcase.